The present invention relates to a method of fabricating a photodiode and the photodiode produced therefrom. Specifically, the present invention is directed to a method of forming a photodiode wherein a layer of N+ polysilicon is formed over a dielectric multilayer of silicon nitride/reoxidized nitride, the silicon nitride layer of the multilayer having been formed on an N+ silicon substrate. A characteristic feature of the inventive photodiode is that on exposure to light photons and, while biasing the N+ silicon substrate positively with respect to the N+ polysilicon layer, the photodiode exhibits negative differential resistance (NDR).
Silicon-based electronic components dominate integrated circuits (IC""s) largely due to a mature and successful silicon processing technology. However, as the technology advances, and as the need for smaller, faster components increases, it is becoming increasingly desirable to combine silicon-based electronic components with silicon-based opto-electronic components to produce opto-electronic integrated circuits (OEIC""s) utilizing existing silicon processing technology.
In OEIC technology, opto-electronic components such as photodiodes characterized by negative differential resistance (NDR) regions are of great interest as they offer a potential for high-speed, high-density and less complex OEIC""s. NDR refers to the rate of change of current through a photodiode as the voltage changes across the diode, upon exposing the photodiode to light.
With their high switching speed and intrinsic binary on-off state, these photodiodes, when combined with other silicon-based electronic devices, potentially will provide highly compact, ultra-fast and low-cost OEIC""s.
Although silicon-based photodiodes are known; see, for example, U.S. Pat. Nos. 4,148,052; 5,241,198; 4,742,027 and 4,534,099, a silicon-based photodiode utilizing a silicon nitride/reoxidized nitride dielectric that demonstrates NDR is not known.
Accordingly, in view of the potential advantages of such photodiodes with NDR characteristics for OIEC""s, it is desirable to provide a photodiode which includes a silicon nitride/reoxidized nitride dielectric utilizing existing silicon-based processing technology.
One object of the present invention is to provide a photodiode that exhibits NDR characteristics.
Another object of the present invention is to provide a photodiode which includes a silicon nitride/reoxidized nitride dielectric.
A further object of the present invention is to provide a photodiode having the above characteristics utilizing existing silicon processing technology.
Specifically, and in one aspect of the present invention, a photodiode is provided that includes at least:
an N+ silicon substrate;
a layer of silicon nitride formed on said N+ silicon substrate;
a layer of, oxidized silicon nitride formed on said silicon nitride layer; and
a layer of N+ polysilicon formed on at least a portion of said oxidized silicon nitride layer, said photodiode exhibiting a negative differential resistance region upon biasing said N+ silicon substrate positively with respect to said N+ polysilicon layer and exposing said photodiode to illumination.
The present invention also provides a method of fabricating a photodiode with NDR characteristics, comprising the stops of:
(a) forming a silicon nitride layer on an N+ silicon substrate;
(b) forming an oxidized silicon nitride layer on said silicon nitride layer; and
(c) forming a layer of N+ polysilicon on at least a portion of said oxidized silicon nitride layer so as to produce a photodiode, wherein said photodiode exhibits a negative differential resistance region upon biasing said N+ silicon substrate positively with respect to said N+ polysilicon layer and exposing said photodiode to illumination.
Throughout the remaining text, the term xe2x80x9creoxidized layerxe2x80x9d is used to denote the oxidized silicon nitride layer. The term xe2x80x9creoxidized layerxe2x80x9d is used herein to distinguish the inventive method, oxidiation of SiN, from conventional oxidation of silicon surfaces.
The present invention also provides an OEIC apparatus which includes at least the photodiode of the present invention as one of components of the OEIC apparatus.